U.S. Pat. No. 7,282,005 B2 describes a hydraulic system for actuating a shifting element of a transmission, having a pilot-controlled control valve device comprising a valve slide and, functionally connected therewith, an also pilot-controlled switching valve device that is also made with a valve slide. By means of a pressure regulating device, the pilot pressure for the control valve device and the switching valve device is set as a function of an electric control signal, such that the pressure regulating device has a defined working pressure range which is usually substantially lower than the actuating pressure of the shifting element. To enable actuating the shifting element with higher pressure values compared with the pilot pressure of the control valve device and the switching valve device, the control valve device is connected downstream from the pressure regulating device, in the area of which the pilot pressure of the pressure regulating device is converted to a higher level.
In general, during the driving operation of a vehicle made with a transmission such as a converter automatic transmission or the like, it must be ensured that in its fully engaged operating condition, a shifting element is operating at its full transmission capacity without slip. For this, at the end of the actuating pressure control pressure range, the actuating pressure is increased abruptly to a higher pressure value, which usually corresponds to a so-termed system pressure. The switch-over or at least approximately abrupt raising of the actuating pressure is effected by means of the switching valve device that is controlled in parallel by the pressure regulating device, which however is only actuated or changed from a first to a second switch condition at high pilot pressures.
By means of the switching valve device, the back-coupling of the actuating pressure to the control valve device is deactivated when the switching valve device is in a second switch condition, so that the control valve device is changed from a so-termed modulation position to an operating condition in which the system pressure applied at the control valve device is completely routed through in the direction toward the shifting element.
Since the valve slide of the control valve device and the valve slide of the switching valve device are respectively arranged in separate valve bores, a hydraulic system, formed in such manner, takes up an undesirably large amount of space.